The use of intravascular medical devices has become an effective method for treating many types of vascular disease. In general, a suitable intravascular device is inserted into the vascular system of the patient and navigated through the vasculature to a desired target site. Using this method, virtually any target site in the patient's vascular system may be accessed, including the coronary, cerebral, and peripheral vasculature.
Catheters are often utilized to place medical devices such as stents and embolic devices at a desired location within the body. A medical prosthesis, such as a stent for example, may be loaded onto a catheter in a configuration having a reduced diameter and then introduced into the lumen of a body vessel. Once delivered to a target location within the body, the stent may then be expanded to an enlarged configuration within the vessel to support and reinforce the vessel wall while maintaining the vessel in an open, unobstructed condition. The stent may be configured to be self-expanding, expanded by an internal radial force such as a balloon, or a combination of self-expanding and balloon expandable.
Balloon catheters are used in a number of endovascular applications including temporarily or permanently occluding blood flow either distal or proximal of a treatment site during neurological examinations, delivering diagnostic agents such as contrast media, assisting in neurovascular embolic coiling of an aneurysm or arteriovenous malformation (AVM), and dilating narrowed blood vessels caused by vasospasm. During therapeutic procedures such as the ones mentioned above, fast aspiration-mediated deflation of the balloon catheter quickly restores sufficient or normal blood flow to the brain in order to avoid potential neurological impairment, such as weakness, loss of sensation, speech problems, etc.
Current single lumen balloon catheters have a few inflation/deflation ports either punched or laser drilled in the polymeric elongated distal shaft. An inadequate seal between the balloon distal tip and the guidewire may lead to blood entering the balloon, which may result in poor balloon visibility and clot formation around the inflation/deflation ports. In an emergency involving a balloon catheter, a physician may be forced to “bail out” by withdrawing the guidewire proximally away from the balloon to instantly deflate the balloon to restore blood flow to the brain. Poor balloon visibility and inability to quickly deflate the balloon during a procedure could lead to vessel damage and other serious complications.
In preparation for use, balloon catheters are flushed with fluid, such as saline. This fluid can be introduced using a syringe connected to a hub, such as a Luer fitting with a rotary selector valve. Air in these parts can be introduced as air bubbles into the balloon catheter during flushing. The difference between the outer diameter of the balloon support member and the inner diameter of the balloon results in the formation of an annular space and air bubble entrapment in the balloon catheter during flushing. Air bubble entrapment is especially problematic in larger diameter compliant and super compliant balloons.
Due to the pressure differential along the longitudinal axis of the balloon catheter, many air bubbles collect in the distal end of the balloon. However, with larger diameter balloons, air bubbles may also collect in the proximal end of the balloon. Collected air bubbles can be larger than 1 mm in diameter and may interfere with visualization of the balloon catheter. Further, air bubble may also dislodge from the balloon in vivo, resulting in air embolisms and strokes. Accordingly, after a balloon catheter is flushed during preparation, its balloon is inflated to a nominal diameter and visually inspected to identify any air bubbles above a certain size, e.g., 1 mm. If more than a predetermined number of such air bubbles are identified, the balloon catheter may be “re-prepped” by repeating the cycle of flushing, inflating, and inspecting. However, re-prepping the balloon catheter may expand the dead spaces in the balloon where air bubbles are entrapped, and the dead spaces may retain air bubbles after several cycles of prepping.
A number of different balloon catheters are known, each having certain advantages and disadvantages. However, there is an ongoing need to provide alternative balloon catheters, in particular, alternative balloon catheters that facilitate isotropic bending and rapid deflation, and methods of making such catheters. There is also an ongoing need to provide alternative balloon catheters with reduced air bubble formation during flushing.